The milestone figure comes only five months after the social network signed up its 400th million user. The pace of its growth has accelerated rapidly - Facebook had only 150 million registered users in January 2009.

If Facebook was a country, its 500 million members would make it the third-largest country in the world.

Facebook, the brainchild of Mark Zuckerberg while he was still studying at Harvard University, launched in February 2004.

To mark the half a billion milestone, the site has launched a new application called ‘Facebook Stories’, a website within Facebook, that encourages users to share their experiences of the social network.

These stories, which are limited to 420 characters, (the same number as a Facebook status update) will then be sorted by location and theme.

The application will also be hosted on several launch partners’ Facebook fan Pages, such as the X Factor and the White House.

Last month, Zuckerberg, Facebook’s founder and chief executive, said it was “almost a guarantee” that the site would hit one billion users, while speaking at the Cannes Lions International Advertising Festival.

He explained: “If we succeed [in innovating and remaining relevant] there is a good chance of bringing this [Facebook] to a billion people…it will be interesting to see how it plays out."

He also revealed that Facebook had just four remaining countries left to conquer: Russia, Japan, China and Korea, according to Zuckerberg.

“We are down to just four counties where we aren’t the leading social network,” he told the Cannes crowd.

The Social Network, a film about Facebook’s rise to prominence is due for release in October 2010. It charts the birth of the site and has the tagline: “You don’t get to 500 million friends without making a few enemies.”

The site recently faced heavy criticism from both European Information Commissioners and users alike, for over-complicated privacy settings, which users said led them unwittingly to make personal information public.

Concerns about privacy on the site were running so high that 60pc of the 1,588 Facebook users questioned by Sophos, a computer security organisation, in May, said that they were considering deleting their accounts on the social networking site.

A further 16pc said they had already stopped using Facebook because they felt they had inadequate control over their data, while a quarter said that they would not be quitting the social networking site, which has almost 500 million users worldwide.

Facebook then bowed to pressure and unveiled a raft of changes to their privacy settings.